Gas diffusion devices and systems have long been used to control the distribution of gas in processes which require aeration treatment. In such processes, the gas diffusion system is located below the liquid surface and is connected to a source of gas supply.
One type of gas diffusion device known in the art is constructed of a porous medium. Numerous small openings in the porous medium break the gas into small bubbles thereby increasing the gas/liquid contact. A drawback of the prior art porous device is that the porous medium has a tendency to clog, thereby reducing or completely stopping the aeration process.
Another type of gas diffusion device known in the art is the hollow-body diffuser, such as that shown in U.S. Pat. No. 4,421,696 to Graue, et al. The Graue et al diffuser is a hollow body having a plurality of slot-shaped ports disposed in a vertical distribution tube through which gas is released. Immediately above the distribution tube is a frustro-conical directional distribution surface upon which the gas streams exiting the ports impinge. The directional distribution surface evenly distributes the gas streams as they rise. The frustro-conical directional distribution surface terminates at a shear edge upon which gas bubbles are dispersed to the liquid. A plurality of drift control vanes are provided to equalize the spread of gas streams exiting each part. While the Graue, et al diffuser has been highly successful in many applications, it has been found that the prior diffuser alone is less than optimum as regards energy use and aeration efficiency in certain applications, such as those requiring deep aeration.